FR2745378A1 - DIFFERENTIAL PRESSURE CONVERTER WITH OVERLOAD PROTECTION SYSTEM - Google Patents

Abstract

Converter in which the faces of the separator discs (6, 7) facing the overload membrane (8) are concave, forming interior chambers (22, 23) of pressurized fluid; each pressure chamber (22, 23) is sealed by a separating membrane (11, 12) movable axially. The measuring mechanism (1, 2, 3) is movable in a cavity (5). Each separator disc (6, 7) comprises a measuring channel (20, 21) located in an eccentric position and traversed by pressurized fluid, this channel being connected at least indirectly to the measuring mechanism (1, 2, 3).

Description

l

Description.

  The invention relates to a measuring pressure difference converter comprising an overload protection system for a measuring mechanism in which the housing of the measuring mechanism is surrounded essentially symmetrically by two separating discs connected integrally with interposition of an overload membrane, and surrounded by a pair of caps forming two pressure chambers to provide the process pressures, in which: 10 - the faces of the separating discs facing the overload membrane are produced with an essentially concave shape by forming internal chambers of pressurized fluid, - the separating discs are crossed perpendicular to the plane of the overload membrane, each time forming a channel of pressurized fluid,

  - each pressure chamber is sealed by a mem-

  separation bran movable axially, with respect to the round

  separation separator, essentially concave in shape, each time constituting an external pressurized fluid chamber, - each time the internal pressurized fluid chamber belonging to a separating disc is connected by the pressurized fluid channel to the chamber external fluid under

  pressure and these chambers are filled with a fluid under pressure

  essentially incompressible.

  Such devices are described in detail

  either by their known use or in the form of publicity

  cation. Their basic mechanical structure is described in a way

  detailed in documents GB-2 065 893 and EP 0 143 702. In-

  depending on the type of conversion of mechanical signals of pressure / pressure differences into equivalent electrical quantities, according to these previous publications, there is provided a substantially cylindrical central body included with suitable sealing means between two caps of the same type, shaped cup. These caps are connected to each other by numerous mechanically prestressed studs, arranged radially; the mechanical preload of the studs is chosen to avoid a pressure loss at the level of the central body for the maximum authorized static pressure load. Due to this mechanical preload necessary in principle, and which varies from one device to another, we arrive at a mechanical preload of the central body.

  tral producing an offset depending on the preload or a deformation of the characteristic curve depending on the preload, the measuring or overload membrane which oc-10 intersects the median plane of the central body. In addition, the seals, ne-

  must be adapted in their composition according to the process fluid and are also subject to wear. Each cap has on the side of the central body,

  a cavity connected by the channels usually in the form of a

  clamping at the connections by flanges. The average distance of these channels is predetermined at the flange connections

by standards.

  The central body asymmetrically comprises a collar to which a head part is fixed; according to document GB 2 065 893, this is provided with means for the conversion of

  the measured value, for processing and display.

  The large number of pressure-tight connection points required in pressure measuring devices

  known, requires in considerable proportions, a usi-

  precision swimming with chip removal for a big name -

number of pieces.

  In addition, according to document WO 88/02107, there is known a pressure measuring device composed of a cylindrical base body provided on one side with tangent flanges between which the pressure sensor is located. This device certainly has a lower number of pressure-tight junction points, but for a fixed mechanical association of display means relative to the position of the device, the mode of

mounting is defined.

  A particular problem with such measuring devices is that of the overload protection system applied to the differential pressure sensor, sensitive, in the event of a unilateral pressure drop, when the static pressure constitutes the differential pressure because it is necessary to protect this

  pressure sensor against damage.

  For this, according to the document Hartmann & Braun, list 10 / 15-6.21, edition October 92, there is known a measurement converter in which the measurement capsule comprising the

  measuring mechanism is suspended centrally, so

  bile axially to an overload membrane, peripheral, sy-

  metric in rotation. However, in practice, such a protection system against overloading of measurement errors dependent on the static pressure, in particular for low pressures.

  differential, so that the increasing deformations of the box

  tier depending on the static pressure, and which develop through the overload membrane to the measuring mechanism, are controlled very largely individually depending on the measuring mechanism, for tolerances,

  does thermal junction processes.

  The present invention therefore aims to develop

  per the overload protection system of a differential pressure transmitter corresponding to the defined type

  above to avoid parasitic influences by con-

  radial lines depending on the absolute pressure in the means of the protection system acting on the measuring mechanism. This problem is solved according to the invention in that: - the measuring mechanism is mounted pendulumly movable in a cavity of the housing of the measuring mechanism and is housed there without constraint and, - each separating disc includes a measuring channel in

  an eccentric position crossed by fluid under pressure

  this channel being connected at least indirectly to the mechanism

nism of measurement.

  According to advantageous developments of the invention

  tion: - the separating discs have an asymmetrical shape in their axial extension,

  - the thickest separating disc contains the cavity of the

  measuring mechanism and, - the measuring mechanism is connected to the separating disc which surrounds it of the internal chamber of pressurized fluid, directly by the measuring channel and by the measuring channel

  of the second separating disc by a tube.

  - the pressurized fluid channel of each separating disc is each provided with a stud which forms an interval

  ring is connected at least on one side to the separate disks

corresponding authors.

  The present invention will be described below using an embodiment shown in the drawing in which the single figure shows in section, the components

  principles of a differential pressure transmitter

tielle described.

  The differential measurement pressure converter

  tielle consists of a central assembly formed by two separation discs 6, 7 between which is a membrane of

  overload 8 preferably welded tightly to the pressure

  if we. The surfaces of the separation discs 6, 7 facing

  the overload membrane 8 have a shape essentially

  cellar and surround with the overload membrane 8, the internal pressure chambers 22, 23, located on each side of

  the overload membrane 8. The exterior surfaces of the devices

  separation plates, opposite to the overload membrane 8,

  essentially concave shape are each welded to a mem-

  separation bran 11, 12 each time forming a chamber

  of pressurized fluid 27, 28 outside. Separation discs

  ration 6, 7 have a central channel of pressurized fluid for connecting the corresponding internal chambers 22, 23 with the corresponding external chambers 27, 28 for the pressurized fluid; each volume formed by an inner chamber 22, 23 and the corresponding outer chamber 27, 28 for the

  pressurized fluid and the associated pressurized fluid channel

  are filled with an essentially pressurized fluid

  compressible. The central assembly is mounted between the caps 17 and 19, forming pressure chambers 24, 25 to provide

process pressure.

  There is also a measuring mechanism 1, 2, 3 composed of sensors for the differential pressure 1, the

  absolute pressure 3 and sensor temperature 2; this mechanic

  nism is connected by a connecting cable 26 to means 17 for processing the measured values. The means for processing the measured values 17 can be supplemented by means

  ensuring the display of measured values. The mechanism of me-

  1, 2, 3 constitutes an integral whole, closed on itself-

  same, and mounted in an electrical passage 4.

  For mechanical fixing, a cavity is provided in a measuring mechanism housing surrounding the measuring mechanism 1, 2, 3; the measuring mechanism 1, 2, 3 is fixed

  pendular and unconstrained in this case. Of my-

  niere detailed it is expected that the measuring mechanism 1, 2, 3 mounted on the electrical passage 4 plunges without contact into the cavity 5; this cavity 5 is closed as a cover or a

  plug by electrical passage 4.

  Advantageously, the mechanical stresses of the housing of the measuring mechanism are absorbed by the electrical passage 4 so that the measuring mechanism 1, 2, 3 can, if necessary, tilt in the cavity 5 while remaining unconstrained. To supply the process pressures to the measuring mechanism 1, 2, 3, each separation disc 6, 7 is provided with a measuring channel 20, 21, offset, traversed by the fluid

  pressure; this channel is connected at least indirectly to the

measuring mechanism 1, 2, 3.

  According to a particular embodiment of the invention, the separation discs 6, 7 are asymmetrical in shape for their axial extension and the thickest disc 6 comprises the cavity 5 receiving the measuring mechanism 1, 2, 3. The measuring channel 21 of the separating disc 6 constitutes a direct connection

  for the pressurized fluid chamber 22, interior, corresponding

  laying, with the interior of the cavity 5 so that the mechanism

  measuring device 1, 2, 3 is rinsed by the pressure fluid in the cavity 5. To connect the measuring mechanism 1, 2, 3 to the

  measuring channel 20 in the separating disc 7, a tube 13 travels

  pours passage 4. The first side of the pressure difference sensor 1 is charged by the pressurized fluid surrounding the

  sensor and giving the process pressure from the chamber

  pressure bre 24 of the cap 18. The second side of the pressure difference sensor 1 is connected by the tube 13, by a flange 14 welded to the separating disc 7 and receives the process pressure from the pressure chamber 25 of the cap 19. The absolute pressure sensor 3 is completely immersed in the pressurized fluid which surrounds the separating disc 6 and it measures the absolute pressure in the pressure chamber 24. The pressure sensor 2 measures the temperature in the immediate vicinity of the absolute pressure sensor 3 and the pressure difference sensor 1. The measuring mechanism is filled each time with a fluid constituting the pressure fluid by a connection

  filling 15, 16 provided in a pressure chamber.

  According to a development of the invention, the studs 9, 10 are placed in the pressurized fluid channels by forming an annular gap. The studs 9, 10 are welded to the separation discs 6, 7 on the side facing the overload membrane 8. This annular interval between the drilling and

  the studs prevents that in the event of an explosion inside the con-

  measurement protector, flames pass through the pressure chambers 24, 25 filled with process gas and surrounded by the

caps 18, 19.

  The sensors 1, 2, 3 are fixed on the passage 4 and

  do not move with the overload diaphragm 8. This sup-

  prime any mobile electrical connection between sensors 1, 2,

  3 and the means 17 for processing the measured values. In or-

  tre, it only requires a single electrical passage 4 waterproof

  pressure. This makes it possible to limit the electrical connections to a minimum

  triques inside the measuring mechanism 1, 2, 3 and having

fewer sealing areas.

  The overload membrane 8 consists of a simple round plane. In addition, asymmetric voltages in the overload membrane 8 are avoided by assembly, transformation or welding methods. In addition, no force is transmitted by the overload membrane 8 to the sensors 1, 2, 3 as is the case for the transducers in

  which sensors 1, 2, 3 form with the sur-

  load 8, an integral assembly or in which the sensors 1, 2, 3 are welded by means of a passage to the overload membrane. During pressure shocks caused for example by the sudden drop in the pressure chamber 25, the pressure of the

  process gas in the pressure chamber 24 causes the

  formation of the separation membrane 11 in the direction of the opposite pressure chamber 25, until its surface on the side of the separation disc presses against the surface of the separation membrane 6. The volume of the fluid chamber under pressure 27, external, corresponding is then reduced to zero. The pressurized fluid contained in the external pressurized fluid chamber 27 then passes through the flame barrier formed by the annular gap remaining between the

  pressurized fluid and the stud 9 housed therein, to the corresponding interior pressurized fluid chamber 22; the overload membrane 8 is thus deformed in the direction of the separation washer 7.

  Effectively, the pressure of the separation membrane 11 is transmitted by the flame barrier acting as a damping element to the overload membrane 8 and then by a measurement channel 21, separated to the sensors 1, 2, 3; the pressurized fluid chamber 22 then functions as a buffer accumulator. This means that the pressure drops act first on the overload membrane 8 and then only via the measurement channels 21 on

  the pressure difference sensor 1, sensitive.

  The absolute pressure sensor 3 detects the pressure

  static pressure of the process fluid. The signal for pressure

  static compensates for faults in the pressure difference sensor

  sion 1, and which depend on the pressure. The temperature-dependent errors for the pressure difference sensor 1 are compensated by the signal from the temperature sensor 2. The compensation is calculated with a processor belonging to the means for processing the measured values 17. The signal

  the static pressure is also corrected and if necessary

  sity, it is transmitted by signal transmission lines, not shown. The assembly formed by passage 4 and sensors 1, 2, 3 can easily be checked before its final assembly. In addition, entering the temperature near sensors 1 and 2 is advantageous for avoiding dynamic temperature errors.

NOMENCLATURE

  1 Pressure difference sensor 2 Temperature sensor 3 Absolute pressure sensor 4 Cavity passage 6.7 Separator discs 8 Overload diaphragm 9.10 Studs 11.12 Separation membranes 13 Tube 14 Flange, 16 Filling nozzles 17 Means of treatment measured values 18.19 Caps, 21 Measuring channel 22.23 Inner chambers of pressurized fluid 24.25 Inner chambers of pressure 26 Connection cable 27.28 Outer chambers of pressurized fluid

Claims (3)

R E V E N D I C A T IONS   1) Compressed measurement pressure difference converter   providing an overload protection system for a   extent to which the housing of the measuring mechanism is surrounded   re essentially symmetrically by two separating discs connected integrally with the interposition of an overload membrane, and surrounded by a pair of caps forming two pressure chambers to provide the process pressures, in which: 10 - the sides of the separating discs facing the overload membrane are produced with an essentially concave shape, forming internal chambers of pressurized fluid, - the separating discs are crossed perpendicular to the plane of the overload membrane, each time forming a channel of fluid under pressure,   - each pressure chamber is sealed by a mem-   separation bran movable axially, with respect to the round   separation separator, essentially concave in shape, each time constituting an external pressurized fluid chamber, - each time the internal pressurized fluid chamber belonging to a separating disc is connected by the pressurized fluid channel to the chamber external fluid under   pressure and these chambers are filled with a fluid under pressure   essentially incompressible, characterized in that - the measuring mechanism (1, 2, 3) is movably mounted   pendulum in a cavity (5) of the housing of the measuring mechanism   safe and is housed there without constraint and, - each separating disc (6, 7) has a measuring channel (20, 21) located in an eccentric position and crossed by   fluid under pressure, this channel being connected at least indirectly   the measuring mechanism (1, 2, 3).   2) Converter according to claim 1, characterized in that - the separating discs (6, 7) have an asymmetrical shape in their axial extension, - the thickest separating disc (6) comprises the cavity (5) of the measuring mechanism (1, 2, 3) and, - the measuring mechanism (1, 2, 3) is connected to the separating disc (6) which surrounds it of the interior chamber of pressurized fluid (22), directly by the measuring channel (23) and through the measuring channel (22) of the second separating disc (7) by a tube (13).   3) Converter according to claim 1, characterized in that - the pressurized fluid channel of each separator disc   (6, 7) is each provided with a stud (9, 10) which forms   mant an annular gap is connected at least on one side to the corresponding separating discs (6, 7). _